1. Field of the Invention
The present invention relates to a subsurface safety valve and, more particularly, to a subsurface safety valve with a simple internal mechanism to provide secondary control fluid communication when the safety valve is locked out.
2. Description of Related Art
Subsurface safety valves are used within wellbores to prevent the uncontrolled escape of wellbore fluids, which if not controlled could directly lead to a catastrophic well blowout. Certain styles of safety valves are called flapper type valves because the valve closure member is in the form of a circular disc, as disclosed in U.S. Pat. No. 3,799,258, or in the form of a curved disc, as disclosed in U.S. Pat. No. 4,926,945. These flappers are opened by the application of hydraulic pressure to a piston and cylinder assembly, as is disclosed in U.S. Re. Pat. No. B14,161,219, to move a flow tube against the flapper. The flow tube is biased by a helical spring in a direction to allow the flapper to close in the event that hydraulic fluid pressure is reduced or lost.
Safety valves of the past have included relatively complicated and thereby expensive to manufacture mechanisms to lock out the safety valve. To "lock out" a safety valve is a term well known to those skilled in the art, and is defined as the ability to temporarily or permanently lock the safety valve's flapper in an open position. A safety valve is locked out when the safety valve fails, such as the seals have failed, or during well workover operations. Once a safety valve is locked out, a secondary or wireline retrievable inset valve is sealably set inside of the longitudinal bore of the safety valve, as described in U.S. Pat. No. 4,252,197, or within a hydraulic communication nipple, and the existing hydraulic control line is used to operate the inset valve.
Previous mechanisms to lock out a safety valve and establish the secondary hydraulic communication pathways added additional length to the safety valve and/or increased the mechanical complexity of the safety valve, thereby increasing the cost of the safety valve. There exists the need for a safety valve with a relatively simple and thereby less costly mechanism to lock out the safety valve.